This invention relates to medical infusion devices that are intended to deliver, in a controlled manner, desired quantities of a fluid to a patient, more particularly this invention relates to the utilization of compliant structures within such medical devices.
Both external and internally implanted infusion pumps are generally known in the art for use in delivering a selected fluid to the body of a patient (i.e. body of a person or animal being treated or benefited by the fluid) in a scheduled or preprogrammed manner. Such fluids include drugs, medications, proteins, e.g. insulin, or the like. Programmable medication infusion pumps offer significant potential advantages to patients who are required to comply with a long-term medication treatment regimen. Such pumps can operate automatically, with little or no patient intervention, to administer an important medication such as insulin to a diabetic patient on a regular basis.
Implantable infusion pumps typically include an internal fluid chamber or reservoir for receiving and storing a supply of the selected fluid (e.g. drug, medication, protein such as insulin) a miniature pump mechanism, programmable control means (e.g. electrical circuit possibly including telemetry elements for communication with an external programming device) for operating the pump mechanism to deliver discrete doses of the fluid from the internal reservoir to a desired region within the body. These pumps typically deliver medication to the body through a catheter connected to an output port of the pump mechanism. A refill port is typically provided on the pump to permit transcutaneous needle access for purpose of periodically refilling the pump reservoir with a fresh supply of fluid. Some implantable infusion pumps include a side port that is connected to the output port of the pump mechanism and to a first end of the catheter. The side port may be used in a process of flushing residue from the catheter, flushing the pump, and or to determine pump stroke volume.
Various infusion pumps, associated components and processes, for example, are described in the various patent publications listed in Table 1, the disclosures of which are hereby incorporated herein by reference. The brief description of each publication is provided in Table 1 to aid the reader in finding specific types of teachings. It is not intended that the incorporation of subject matter be limited to those topics specifically indicated, but instead the incorporation is to include all subject matter found in these publications. The teachings in these incorporated publications may be combined with the teachings herein in many ways.
Operation of these pumps may be effected by a combination of flow resistance within a fluid path and a characteristic known as xe2x80x9ccompliancexe2x80x9d. Flow resistance is related to how much pressure is required to make a desired quantity of fluid flow through the path in a given time period. Compliance is related to how a fluid path, as defined by the structural body forming the path or a part of the path, expands, contracts or deflects under an environmental input, such as, for example, a pressure load from a pulse stroke from an infusion pump mechanism that is intended to deliver an amount of medication to a catheter.
If a particular flow path (e.g. path from pump mechanism output port to distal end of a catheter) has little or no compliance, any attempt to move fluid into the flow path (e.g. at the pump mechanism output port) will only occur to the extent that substantially an equivalent amount of fluid will be moved out of the flow path (e.g. out of the distal end of the catheter). On the other hand, if a flow path offers a large amount of compliance, a fluid may be easily pushed into one end of the flow path, during a specified time period, with little or no fluid exiting the other end of the flow path during that time period.
In some pump designs too little compliance may influence the infusion pump""s performance by offering increased resistance of flow at the inlet of the flow path (e.g. output port of the pump mechanism). If a significant amount of resistance is offered, the infusion pump mechanism may deliver less fluid, than predicted, for each pump stroke. It is further known that excessive compliance may influence the infusion pump mechanism""s performance by offering insufficient resistance to flow at the inlet of the flow path (e.g. output port of the pump mechanism). If an insufficient amount of resistance is offered, it may result in delivery of more fluid, than predicted, with each stroke. Either situation may provide incorrect dosing of the fluid, which may have long term and short term health effects for a patient being treated by the fluid.
In some pump designs, especially with implantable pumps, low power consumption is of importance so that battery life is not prematurely reduced below an acceptable level and that useful life of the pump is of reasonable length. In electromagnetic pumps, such as those described in U.S. Pat. No. 5,797,733, as referenced in Table 1, it is desirable that the electromagnetic coil be activated for only for a short period of time, with only a limited amount of power so as to minimize battery drain. However, if an inappropriate amount of compliance exists, a piston that is used to force fluid from a fluid reservoir may not travel an intended length and thus may not cause a desired amount of material to be dispensed.
In the ""733 patent, as illustrated in FIG. 4 of this referenced patent, it is proposed that an accumulator 436 form a portion of the flow path between the outlet tube 430 of the pump 420 and the catheter 440. It is proposed that this accumulator be in the form of a small compliant element. It is indicated that the accumulator 436 can comprise a small length of Silicone rubber tubing, i.e. about xc2xd inch in length and {fraction (1/32)} inch inner diameter.
Among other things, the ""733 patent further indicates that
xe2x80x9c . . . a small accumulator is provided downstream of the pump outlet orifice large enough to contain the pulse volume of the pump with a reasonable pressure rise. The catheter diameter may then be small enough to ensure that the flow through the accumulator catheter combination is critically damped and no flow oscillations occur which might otherwise draw additional flow through the pump check valves. It is desirable that the accumulator be small enough so that a significant pressure rise occurs during the pump stroke. The back pressure build-up serves the purpose of preventing a large pulse volume when the supply pressure exceeds the delivery pressure.xe2x80x9d
However, even with some recognition of a need for an appropriate amount of compliance in the pump system, a need continues to exist in the art for improved methods of and apparatus for supplying compliance within infusion pump systems and particularly within implantable systems.
The use of silicone as a source of compliance within a fluid path, and especially for long term use, has many shortcomings: (1) It is subject to swelling, leakage, and change of mechanical properties, as it is permeable to water, air, and various other substances, such as preservatives that may be used with various types of insulin; (2) The compliance of silicone is based on its flexibility as opposed to its compressibility; (3) It is a hydrophobic material can aggravate physical instability of some drugs, e.g. insulin, which can lead to precipitation and build up of the drug within the system; (4) If exposed to body fluids, hard tissue may build up on the tubing to reduce its compliance with the progression of time; (5) If exposed to ambient pressure within the body, unintentional discharge of fluid may occur as a result of an impact, other significant pressure increase, or shock to the source of compliance; (6) If used within a portion of the system subject to high pressure flushing, the silicone may rupture.
In view of the shortcomings noted above, it is a first object of the present invention to provide a source of compliance that is not permeable to fluids that it may come into contact with.
It is a second object of the present invention to provide a source of compliance that is compressible.
It is a third object of the invention to provide a source of compliance that is less likely to cause physical instability of the drugs that it will come into contact with, e.g. insulin.
It is a fourth object of the invention to provide a source of compliance that is less variable with the passage of time.
It is a fifth object of the invention to provide a source of compliance that is less likely to cause unintentional discharge of fluid into the body of a patient.
It is a sixth object of the invention to provide a source of compliance that is not subject to damage as a result of exposure to high pressures that might occur, for example, during a flushing operation, or the like.
It is intended that each of the above noted objects of the invention, as well as any other objects of the invention set forth explicitly or implicitly herein, be pursued alone, or in various combinations, by different aspects of the invention. It is further intended that additional objects of the invention provide infusion pumps that pursue or address one or more of the above noted objects of the invention alone or various combinations.
A first aspect of the invention provides an infusion pump for delivering a fluid to the body of a patient, including: (1) a pumping mechanism having a fluid entrance port and fluid exit port for transferring fluid from the entrance port to the exit port, (2) a reservoir for containing the fluid, the reservoir connected to the entrance port of the pumping mechanism by a first fluid path, (3) an outlet connected to the exit port of the pumping mechanism along a second fluid path for supplying fluid from the reservoir to the body of a patient, (4) a control device for controllably operating the pumping mechanism, (5) a source of compliance in communication with fluid along the first or second fluid paths for providing a source of compliance for fluid in proximity to the entrance port of the pump mechanism or for fluid exiting the exit port of the pumping mechanism, respectively. The source of compliance includes a structure selected from the group of (a) a compressible structure, (b) an expandable structure, (c) a non-permeable structure, and (d) a structure located within a flow path defined by a substantially non-compliant material.
A second aspect of the invention a method for infusing a fluid into a body of a patient, including: (1) providing fluid to a reservoir within an infusion device, (2) controlling a pumping mechanism having a fluid entrance port and fluid exit port for transferring fluid from the entrance port to the exit port, (3) directing a fluid from the reservoir to the entrance port of the pumping mechanism along a first fluid path, (4) directing fluid to an outlet connected to the exit port of the pumping mechanism along a second fluid path for supplying to the body of a patient, (5) operating the pumping mechanism in a controlled manner, (6) supplying a source of compliance in communication with fluid along the first or second fluid paths for providing a source of compliance for fluid in proximity of the entrance port of the pump mechanism or for fluid exiting the exit port of the pumping mechanism, respectively. The source of compliance includes a structure selected from the group of (a) a compressible structure, (b) an expandable structure, (c) a non-permeable structure, and (d) a structure located within a flow path defined by a substantially non-compliant material.
A third aspect of the invention provides an infusion pump for delivering a fluid to the body of a patient, including: (1) a pumping means having a fluid entrance port and fluid exit port for transferring fluid from the entrance port to the exit port, (2) a means for containing a fluid to be dispensed connected to the entrance port of the pumping means by a first fluid path, (3) an outlet means connected to the exit port of the pumping mechanism along a second fluid path for supplying fluid from the reservoir to the body of a patient, (4) a means for controllably operating the pumping mechanism, (5) a compliance means in communication with fluid along the first or second fluid paths for providing a source of compliance for fluid in proximity to the entrance port of the pump mechanism or for fluid exiting the exit port of the pumping mechanism, respectively. The compliance means includes a structure selected from the group of (a) a compressible structure, (b) an expandable structure, (c) a non-permeable structure, and (d) a structure located within a flow path defined by a substantially non-compliant material.
A fourth aspect of the inventions provides a compliance mechanism for use with a pump mechanism in an infusion pump that is intended to deliver a predetermined amount of fluid through an outlet from operation of the pump mechanism. The compliance mechanism includes at least one pillow. The at least one pillow includes a pair of diaphragms that are hermetically sealed to enclose a known volume of a gas or other compressible substance. The at least one pillow is positioned to be in fluid communication with fluid in the infusion pump.
A fifth aspect of the invention a compliance mechanism for use with a pump mechanism in an infusion pump that is intended to deliver a predetermined amount of fluid through an outlet from operation of the pump mechanism. The compliance mechanism includes a drum member including a pair of diaphragms that are hermetically sealed to open ends of a stand off member.
The drum encloses a trapped volume of gas or other compressible substance and is positioned to be in fluid communication with the fluid in the infusion pump.
A sixth aspect of the invention provides a compliance mechanism for use with a pump mechanism in an infusion pump that is intended to deliver a predetermined amount of fluid through an outlet from operation of the pump mechanism. The compliance mechanism includes (1) at least one diaphragm, and (2) a body having a cavity with at least one opening, wherein the at least one diaphragm is hermetically sealed to close off the at least one opening in the cavity. The diaphragm is positioned to be in fluid communication with the fluid in the infusion pump.
A seventh aspect of the invention provides an infusion pump for delivering a fluid to the body of a patient, including: (1) a reservoir for containing a fluid to be dispensed, (2) an outlet for supplying fluid from the reservoir to the body of a patient, (3) a pumping mechanism for transferring fluid from the reservoir to the outlet (4) a programmable control device, including an electrical circuit, for controllably operating the pumping mechanism, and (5) a compressible structure in communication with fluid in the infusion pump for providing a source of compliance within the infusion pump.
While certain aspects of the invention have been noted above, other aspects will be apparent to those of skill in the art upon study of the teachings herein. As noted above, it is not intended that each aspect of the invention simultaneously address all of the objectives set forth above. Each aspect of the invention may address a single one of the objectives or alternatively may address a combination of two or more objectives.
Some preferred embodiments provide implantable infusion pumps with sources of compliance positioned between an exit port of a pumping mechanism and an outlet (e.g. an opening in a catheter) of the infusion pump. Other embodiments provide compliance for fluid in an entrance port of the pumping mechanism. Insertion of compliance in a flow path that is down stream of the pumping mechanism may aid in minimizing negative effects associated with attempting to force fluid through a restricted flow path that is further down-stream, such as that offered by a catheter or other outlet component. Insertion of compliance before the pumping mechanism may aid in reducing negative effects associated with an up stream restricted flow path, such as that which might be offered by a rigid filter located between the reservoir and the pumping mechanism. Several structural components, assemblies, or configurations are used as sources of compliance. For example, compressible structures (e.g. pillows, drums) are used within a side port of the infusion pump. The compressible structures may quickly distort to accommodate for a large impulse of fluid into the flow path that can not otherwise be readily dealt with. The compression, in turn, results in a restoring force being exerted that returns the structure substantially to its original volume so as to slowly force fluid from the flow path.
Thus, some embodiments of the present invention provide an attachable, field replaceable catheter assembly with controlled compliance characteristics for use with an implantable infusion pump that attempts to deliver an amount of fluid in a short time period. However, to minimize energy consumption, it is typically desired to operate the pumping mechanism over a time period that is significantly less than that necessary to delivery a desired volume of fluid from an outlet of the infusion pump. The supplied compliance aids in ensuring that a desired amount of fluid is deliver for each operation of the pumping mechanism (e.g. each stroke of an electromagnetically driven piston).
According to one embodiment of the invention, a compliance mechanism is used with a pump mechanism in an infusion pump to aid in delivering a desired or predetermined amount of fluid through a catheter. The compliance mechanism includes a plurality of diaphragms used in the formation of at least one pillow. Each of the at least one pillows is formed from a pair of diaphragms that are hermetically sealed to enclose a known volume of a gas. The at least one pillow is preferably located within a fluid path that is separated from an exit port of the pump mechanism by a small amount of flow impedance, or resistance, so as to minimize the effects of flow resistance in the catheter.
In some embodiments, the compliance mechanism includes a support component to protect the at least one pillow from collapse beyond its structural limits during the pump stroke or during a flush out operation. Further embodiments provide pillows which can accommodate pressures up to about xe2x88x928 to about 300 psi. Still further embodiments, form the diaphragms from a metallic material, such as titanium or the like, a metallic composite, or Halar film.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of embodiments of the invention.